1. Technical Field
This disclosure relates to mobile communications and more particularly, to a mobile communication device with increased transmitter power efficiency.
2. Description of the Related Art
Portable communications systems typically rely on radio frequency transmissions that are sent and received using antennas. Conventional mobile phones employ a whip antenna for receiver functions and transmitter functions on a shared basis. The receive and transmit circuits are accommodated to provide both the receive and transmit functions through the same antenna.
Referring to FIG. 1, a schematic diagram of a portion of a mobile phone 10 is shown. Mobile phone 10 employs a receiver/transmitter (Rx/Tx) whip antenna 11 with a duplexer or switch 12. Duplexer 12 permits access to both receiver circuitry 14 and transmitter circuitry 16. Receiver circuitry 14 includes a low noise amplifier (LNA) 18 which receives a radio frequency signal. A band pass filter (BPF) 20 filters the signal. A mixer 22 mixes the filtered signal with a signal from a local oscillator 24 to output an intermediate frequency (IF) signal on a line 26. The received signal is processed as is known in the art.
Transmitter (Tx) circuitry 16 includes an inphase/quadrature (I/Q) modulated signal 28 which is mixed by mixer 30 with a signal from local oscillator 24. The mixed signal is amplified by a power amplifier driver 32 and then filtered by a band pass filter (BPF) 34. The filtered signal is then amplified by a power amplifier 36. After being amplified by amplifier 36, the signal is transmitted from antenna 11. Referring to FIG. 2, other prior art designs have employed separate (dedicated) patch antennas 40 and 42 for receiving and transmitting signals, respectively.
These typical antenna arrangements of mobile phones, include a Tx power amplifier 36 which is always ON (OFF in stand-by mode) and is working with a wide range of transmit power levels controlled by the infrastructure of mobile phone networks. Tx power amplifier 36 typically has maximum power efficiency at the maximum Tx power output levels. Correspondingly, operating at lower Tx power levels means low efficiency for the Tx power amplifier.
Proposed suggestions to address the efficiency problem have included implementing switches or linearization techniques. Linearization techniques include employing non-linear amplification which is more power efficient and then applying a linear scheme. Such techniques suffer from high implementation costs for transmission circuitry. Therefore, a need exists for a portable communication device which provides high power efficiency without high costs for transmission circuitry. Less power usage is desirable, which in mobile phone systems, increases talk time, for example.
A transmission portion of a front end for a portable communication device, in accordance with the present invention, includes a first transmission antenna coupled to a first output of a branching device for transmitting signals having a power below a threshold value. A power amplifier is coupled to a second output of the branching device. The power amplifier provides amplification to signals to be transmitted. A second transmission antenna is connected to an output of the power amplifier such that the power amplifier is switched off for transmission signals having a power below the threshold value and switched on to amplify transmission signals above the threshold value.
A front end for a portable communication device, in accordance with the present invention, includes a transmission portion having a first transmission antenna coupled to a first output of a branching device for transmitting signals having a power below a threshold value, and a power amplifier is coupled to a second output of the branching device. The power amplifier provides amplification to signals to be transmitted, and a second transmission antenna is connected to an output of the power amplifier such that the power amplifier is switched off for transmission signals having a power below the threshold value and switched on to amplify transmission signals above the threshold value. A receiver portion includes a receiver antenna coupled to a receive mixer for receiving signals for the front end. A local oscillator is included for providing signals to down convert the received signals and up convert the transmission signals for the front end.
In alternate embodiments, the first and second antennas may include patch antennas, embedded antennas or other types of antennas. The branching device may include a switch or a splitter. The communication device may include a mobile phone, a two-way pager, a personal digital assistant, or other transmitter device. The mobile phone may include a code division multiple access phone having a transmission power range of about 80 decibels. The power amplifier may provide a gain of 30 decibels and the threshold value is about 30 decibels below a largest transmission value of the transmission power range. The power amplifier may provide a gain G and the threshold value is less than a largest transmission value of the transmission power range minus G. A power sensor may be adapted for sensing a power level of received signals and outputs an enable signal to switch the power amplifier on when the sensed power is below a value, and disables the power amplifier when the sensed power is above the value. The transmission portion may further include a coupler adapted for sensing a power level at an output of the power amplifier for switching the power amplifier off when the sensed power is below a value and enabling the power amplifier when the sensed power is above the value.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.